Conventionally, in the image forming apparatus using the electrophotographic type process, for example, a surface of an electrophotographic photosensitive member (photosensitive member) is charged by a charger and thereafter, the charged surface of the photosensitive member is exposed to light in accordance with image information, so that an electrostatic latent image is formed on the surface of the photosensitive member. As for the charger for charging the surface of the photosensitive member, a corona discharger (corona discharge generator) is widely used.
Generally, a discharging electrode of the corona discharger is made of an electroconductive member such as a metal and is disposed spaced from the photosensitive member by the predetermined gap. By applying a high voltage to the discharging electrode, the photosensitive member as the member to be charged is charged using the discharge from the discharging electrode.
The shape of the discharging electrode is needle configuration having multiple needle-like electrodes (needle-like electrode array), a wire configuration in which wire per se is used as the electrode, or a strip configuration. The discharging electrode is repeatedly used, and therefore, the discharging electrode may be contaminated by foreign matter which may disturb the discharge.
Patent document 1 is directed to the problem in which the discharging electrode is contaminated by foreign matter such as silica with the result of disturbance to the corona discharge, and proposes that the surface of the discharging electrode is coated with film of carbon including diamond (carbon film which is a film made of a material comprising carbon). Such a carbon film is capable of suppressing the deposition of the foreign matter to the discharging electrode and enhancing the durability of the discharging electrode, and therefore, it is effective as a surface layer constituting a protection layer for the discharging electrode.